lwip: Support for linux target

Implement linux port layer and reuse the original FreeRTOS layer
that's compiled and used on linux target as well, by means of FreeRTOS
simulator.

components/lwip/port/include/netinet/in.h

@@ -0,0 +1,14 @@
+/*
+ * SPDX-FileCopyrightText: 2015-2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef IN_H_
+#define IN_H_
+
+#include "lwip/inet.h"
+
+#define IN6_IS_ADDR_MULTICAST(a)    IN_MULTICAST(a)
+
+#endif /* IN_H_ */